Taser have been trialled and welcomed by police forces across the world, many of which have been looking for a weapon that is less lethal than a firearm.

Amnesty has called for the stun guns, which administer a high voltage shock of electricity that incapacitates a person, to be treated as "potentially lethal weapons".

The lobby group says that Taser guns have been linked to 70 deaths in the US and should only be used in extreme cases.

"We are disheartened at Amnesty's rhetoric and continued misrepresentation of the facts regarding Taser devices," Mr Smith said.

The company said on Wednesday that an independent study had found its guns are "relatively safe".

However, in its report the Potomac Institute added that it "strongly recommends that additional research be conducted at the organism, organ, tissue, and cell levels" so it could better understand the effects of the stun guns.